Fuel injection valve

ABSTRACT

A fuel injection valve, in particular an injection valve for fuel injection systems of internal combustion engines, is made of a piezoelectric or magnetostrictive actuator and a valve closing body that can be set in motion by the actuator via a valve needle and that interacts with a valve seat surface to produce a seat. To compensate for the temperature expansion, at least one damping element made of a solid is present and exhibits an almost static behavior at a high deformation rate and is elastically or plastically deformable at a low deformation rate.

FIELD OF THE INVENTION

The present invention relates to a fuel injection valve.

BACKGROUND INFORMATION

Usually changes in the length of a piezoelectric actuator of a fuelinjection valve caused by temperature influences are compensated for viahydraulic devices or by selecting suitable combinations of materials.

A fuel injection valve in which the change in length of the actuator iscompensated for by an appropriate combination of materials is known fromGerman Patent No. 197 02 066. The fuel injection valve arising from thispublication has an actuator that is conducted in the valve housing underspring prestress and that interacts with an actuating part made of anactuating body and a head part, the head part lying on the piezoelectricactuator and the actuating body penetrating an inner recess of theactuator. The actuating body is operably connected to a valve needle.When the actuator is set in motion, the valve needle is actuated againstthe direction of spraying.

The actuator and the actuating body have at least approximately the samelength and are made of a ceramic material or of a material similar toceramic with respect to its thermal expansion. The result of usingmaterials having the same lengths and thermal expansion coefficients,e.g., INVAR, is that the actuator and the actuating body expanduniformly under the influence of heat and thus do not have an adverseeffect on the opening and closing times. An undesired opening of thefuel injection valve between the switching pulses is also avoided.

The disadvantage of this arrangement is above all its limited usabilityin systems that are subject to large fluctuations in temperature. Thearrangement known from German Patent No. 197 02 066 does not achieve theobjective due to the nonlinear behavior of the temperature expansioncoefficients of piezoelectric ceramics over the temperature curve. As aresult, imprecise fuel metering times and amounts occur.

Another disadvantage is the high manufacturing effort required, which isassociated with relatively high costs caused in particular by theselection of the materials (e.g., INVAR).

SUMMARY OF THE INVENTION

The fuel injection valve of the present invention with thecharacterizing features of the main claim, on the other hand, has theadvantage that the temperature compensation is independent of thethermal expansion coefficient of the piezoelectric ceramic. The thermalexpansion is compensated for via damping elements having aspeed-dependent transmission behavior for arriving pulses and is thusindependent of the selection of the material for the actuating elementand valve housing. Thus a secure and precise method of operation of thefuel injection valve is assured.

Advantageous further developments of the fuel injection valve indicatedin the main claim are possible by implementing the measures listed inthe subclaims.

The simple design of the components from the point of view ofmanufacturing technology is advantageous. In particular the enclosingand prestressing of the actuator in an actuator housing areadvantageous, since the thermal change in length of the actuator doesnot need to be compensated for by expensive material combinations, butis compensated for by a prestress spring. Thus the entire length of theactuator housing is unaffected by thermal changes in length. Thus byuncoupling the actuator and the valve housing, only a change in positionof the actuator housing relative to the valve housing still needs to becompensated for.

The enclosing of a readjusting spring and damping element in a valveshell is also advantageous because of the resulting compactconstruction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an axial section through a first exemplary embodiment of afuel injection valve of the present invention.

FIG. 2 shows an axial section through a second exemplary embodiment of afuel injection valve of the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a first exemplary embodiment of fuel injection valve 1 ofthe present invention in axial section. This is a fuel injection valve 1that opens inwards.

Ring-shaped actuator 3 having central recess 7 made of disk-shapedpiezoelectric or magnetostrictive elements 4 and prestress spring 5 arearranged in actuator housing 2. Actuator 3 is operated by an electroniccontrol unit via a plug contact (not shown). For the sake ofsimplification, only a single connection wire 6 is shown in FIG. 1.

Actuator housing 2 is made of shell 8 and actuator housing cover 9.Actuator housing cover 9 rests against first end 10 of prestress spring5. First face 11 of actuator 3 rests against an end of shell 8 on thespraying side, actuator 3 being surrounded radially by shell 8. Secondface 12 of actuator 3 and second end 13 of prestress spring 5 aresupported against intermediary center flange 14. Actuator 3 isprestressed by prestress spring 5 via shell 8.

Center flange 14 is preferably connected frictionally with actuatingbody 16 by welded seam 15. Actuating body 16 is arranged in centralrecess 7 of actuator 3 and is connected to valve needle 17 on whichvalve closing body 18 is formed. When valve closing body 18 is liftedaway from valve seat surface 19, fuel is sprayed through spray aperture20 formed in valve seat body 29. Actuating body 16 is supported at itsend against readjusting spring 21. The fuel flows to the seat via fuelinlet 22 of valve housing 23 formed close to the seat and via space 24between valve needle 17 and valve housing 23.

First ring-shaped damping element 25 a is located at first end 39 ofactuator housing 2, between shell 8 of actuator housing 2 and valvehousing 23. Second ring-shaped damping element 25 b is located at secondend 40 of actuator housing 2, between actuator housing cover 9 ofactuator housing 2 and valve housing 23. Damping elements 25 a, 25 b aremade of a plastic, in particular of uncured silicone rubber, whichexhibits an almost static behavior at a high deformation rate and iselastically or plastically deformable at a low deformation rate. Dampingelements 25 a, 25 b have mechanical springs 27 whose damping behavior issuperimposed on the damping behavior of the plastic. The plastic isadvantageously enclosed in jacket 26. Damping elements 25 a, 25 b bufferactuator housing 2 against valve housing 23.

When an electrical activating voltage is applied to actuator 3 of fuelinjection valve 1 of the present invention shown in FIG. 1, disk-shapedelements 4 of actuator 3 expand, causing center flange 14 to be movedagainst the direction of flow of the fuel. Prestress spring 5 iscompressed further against the prestress already present. Valve closingbody 18 lifts from valve seat surface 19 and fuel is sprayed throughspray aperture 20 formed in valve seat body 29.

During the operation of fuel injection valve 1 of the present inventionin an internal combustion engine, the high actuating frequency ofactuator 3 causes damping elements 25 a, 23 b located between valvehousing 23 and actuator housing 2 to behave like an incompressiblesolid, since when actuator 3 is set in motion it expands too fast fordamping elements 25 a, 25 b to be compressed. The behavior of dampingelements 25 a, 25 b is almost static, causing the pulse initiated by theelectrical activating voltage to be transmitted to actuating body 16 andfuel injection valve 1 to open.

Fuel injection valve 1 experiences severe temperature fluctuationsduring operation. On the one hand, the entire fuel injection valve 1 isheated by contact with the combustion chamber of an internal combustionengine; on the other hand local temperature changes occur caused, e.g.,by the power loss during deformation of piezoelectric actuator 3 or byelectrical charge movement. This results in a thermal shortening inlength of disk-shaped elements 4, since piezoelectric ceramics havenegative temperature expansion coefficients, i.e., they contract whenheated and expand when cooled.

Such a shortening of actuator 3 by heating is compensated for withinactuator housing 2 by the expansion of prestressed spring 5. Theshortening of actuator 3 leads to an elongation of prestress spring 5.Since center flange 14 is arrested at actuating body 16 via welded seam15, a change in position of actuator housing 2 results from the changein length of actuator 3. This change in position of actuator housing 2is compensated for by the buffering of actuator housing 2 within valvehousing 23 by damping elements 25 a, 25 b, since, during the quasistaticstatic changes in position of actuator housing 2 relative to valvehousing 23 due to temperature influences, actuator housing 2 moves soslowly that damping elements 25 a, 25 b are deformed elastically orplastically.

FIG. 2 shows in an axial section a second exemplary embodiment of fuelinjection valve 1 of the present invention. Already described elementsare provided with corresponding reference numbers, so that a repeateddescription is unnecessary.

In this exemplary embodiment, actuator 3 rests at its second face 12against actuator housing cover 30, against which prestress spring 5 issupported and is clamped between actuator housing cover 30 and valvehousing cover 28. Actuator 3 is supported at its first face 11 againstflange 31, which is operably connected to valve housing 23 by weldedseam 32. Actuating body 16 is mounted on actuator housing cover 30 andis conducted through central recess 7 of actuator 3.

Actuating body 16 projects at one end into valve shell 33. In valveshell 33 readjusting spring 21 and damping element 25 are enclosed sothat readjusting spring 21 and damping element 25 are supported againstintermediary valve needle flange 34. Readjusting spring 21 is clampedbetween cover plate 38 of valve shell 33 and valve needle flange 34.Valve needle flange 34 and valve needle 17, which projects throughrecess 35 in base plate 37 of valve shell 33, are formed in one piece.Valve needle 17 is conducted through valve needle guide 36. Valveclosing body 18, which forms a seat with valve seat surface 19, formsthe termination of valve needle 17. The fuel is fed via a lateral fuelinlet 22 and flows to the seat via space 24 between valve needle 17 andvalve housing 23. At least one spray aperture 20 is formed in valve seatbody 29.

When an electrical activating voltage is applied to actuator 3 of fuelinjection valve 1 of the present invention, piezoelectric elements 4 ofactuator 3 expand. Since actuator 3 at its first face 11 rests againstflange 31, which is connected permanently to valve housing 23 via weldedseam 32, it expands in the lift direction and entrains actuating body 16in the lift direction. Due to the hard transmission behavior of dampingelement 25, actuating body 16, operably connected to valve shell 33,entrains valve needle 17 via valve needle flange 34 and thus opens fuelinjection valve 1.

The hard transmission behavior of damping element 25 is caused by thehigh switching speed of actuator 3. When actuator 3 is set in motion,actuating body 16 moves so quickly that damping element 25 behaves likean incompressible solid and transmits the pulse to valve needle flange34 and valve needle 17. However, fuel injection valve 1 is also subjectto a heat expansion. During this slow change in length of actuator 3,damping element 25 exhibits a soft transmission behavior. When actuatingbody 16 is displaced by a quasi-static thermal that change in length ofactuator 3, the movement is compensated for by damping element 25 inthat damping element 25 is compressed and valve closing body 18 ispressed against valve seat surface 19 by prestress spring 5 via valveneedle flange 34.

The present invention is not limited to the exemplary embodiments shown;it can also be implemented with a plurality of other constructions offuel injection valves 1.

What is claimed is:
 1. A fuel injection valve, comprising: one of apiezoelectric actuator and a magnetostrictive actuator; a valve needle;a valve seat surface; a valve closing body that can be activated by theone of the piezoelectric actuator and the magnetostrictive actuator viathe valve needle and that interacts with the valve seat surface toproduce a sealing seat; and at least one damping element including asolid that exhibits an almost static behavior at a high deformation rateand is one of elastically deformable and plastically deformable at a lowdeformation rate.
 2. The fuel injection valve according to claim 1,wherein: the fuel injection valve corresponds to an injection valve fora fuel injection system of an internal combustion engine.
 3. The fuelinjection valve according to claim 1, wherein: the solid of the at leastone damping element includes a plastic.
 4. The fuel injection valveaccording to claim 3, wherein: the plastic includes an uncured siliconerubber.
 5. The fuel injection valve according to claim 3, wherein: theat least one damping element includes a mechanical spring exhibiting adamping behavior that is superimposed on a damping behavior of theplastic.
 6. A fuel injection valve, comprising: one of a piezoelectricactuator and a magnetostrictive actuator; a valve needle; a valve seatsurface; a valve closing body that can be activated by the one of thePiezoelectric actuator and the magnetostrictive actuator via the valveneedle and that interacts with the valve seat surface to produce asealing seat; at least one damping element including a solid thatexhibits an almost static behavior at a high deformation rate and is oneof elastically deformable and plastically deformable at a lowdeformation rate; a shell; an actuator housing including an actuatorhousing cover; a prestress spring; and a center flange, wherein: a firstface of the one of the piezoelectric actuator and the magnetostrictiveactuator is supported against the shell, the prestress spring rests witha first end against the actuator housing cover that terminates the shellto produce the actuator housing, and a second face of the one of thepiezoelectric actuator and the magnetostrictive actuator and a secondend of the prestress spring are supported against the center flange. 7.The fuel injection valve according to claim 6, further comprising: avalve housing, wherein: the at least one damping element includes afirst ring-shaped damping element and a second ring-shaped dampingelement, and the actuator housing together with the one of thepiezoelectric actuator and the magnetostrictive actuator containedtherein and the prestress spring has a constant length and is supportedagainst the valve housing with another first end via the firstring-shaped damping element and with another second end via the secondring-shaped damping element.
 8. The fuel injection valve according toclaim 6, wherein: the valve needle is connected to the center flange viaa welded seam.
 9. A fuel injection valve, comprising: one of aPiezoelectric actuator and a magnetostrictive actuator; a valve needle;a valve seat surface; a valve closing body that can be activated by theone of the piezoelectric actuator and the magnetostrictive actuator viathe valve needle and that interacts with the valve seat surface toproduce a sealing seat; at least one damping element including a solidthat exhibits an almost static behavior at a high deformation rate andis one of elastically deformable and plastically deformable at a lowdeformation rate; a flange; and a cover plate, wherein: the one of thepiezoelectric actuator and the magnetostrictive actuator is supportedwith a first face thereof against the flange and with second facethereof against the cover plate.
 10. The fuel injection valve accordingto claim 9, further comprising: a valve housing, wherein: the flange isconnected to the valve housing via a welded seam.
 11. The fuel injectionvalve according to claim 9, further comprising: a valve shell; and anactuating body supported at one end against the cover plate and beingoperably connected to the valve needle via the valve shell.
 12. The fuelinjection valve according to claim 11, further comprising: a readjustingspring; and a flange of the valve needle, wherein: the valve shellincludes a cover plate and a base plate, the readjusting spring and theflange of the valve needle are enclosed in the valve shell, the at leastone damping element is arranged between the flange of the valve needleand the base plate of the valve shell, and the readjusting spring isclamped between the flange of the valve needle and the cover plate ofthe valve shell.
 13. The fuel injection valve according to claim 12,wherein: a recess, through which the valve needle extends, is located inthe base plate of the valve shell.
 14. A fuel injection valve,comprising: one of a Piezoelectric actuator and a magnetostrictiveactuator; a valve needle; a valve seat surface; a valve closing bodythat can be activated by the one of the piezoelectric actuator and themagnetostrictive actuator via the valve needle and that interacts withthe valve seat surface to produce a sealing seat; at least one dampingelement including a solid that exhibits an almost static behavior at ahigh deformation rate and is one of elastically deformable andplastically deformable at a low deformation rate; an actuating body thatacts on the valve needle, wherein: the one of the piezoelectric actuatorand the magnetostrictive actuator is ring-shaped and includes a centralrecess through which extends the actuating body.
 15. The fuel injectionvalve according to claim 1, wherein the at least one damping element hasa ring shape and compensates for thermal expansion of the at least oneof the piezoelectric actuator and the magnetostrictive actuator.
 16. Thefuel injection valve according to claim 1, wherein the at least onedamping elements is disk shaped and includes a mechanical spring.